Surface Curvature Differentially Regulates Stem Cell Migration and Differentiation via Altered Attachment Morphology and Nuclear Deformation.

Signals from the microenvironment around a cell are known to influence cell behavior. Material properties, such as biochemical composition and substrate stiffness, are today accepted as significant regulators of stem cell fate. The knowledge of how cell behavior is influenced by 3D geometric cues is, however, strongly limited despite its potential relevance for the understanding of tissue regenerative processes and the design of biomaterials. Here, the role of surface curvature on the migratory and differentiation behavior of human mesenchymal stem cells (hMSCs) has been investigated on 3D surfaces with well-defined geometric features produced by stereolithography. Time lapse microscopy reveals a significant increase of cell migration speed on concave spherical compared to convex spherical structures and flat surfaces resulting from an upward-lift of the cell body due to cytoskeletal forces. On convex surfaces, cytoskeletal forces lead to substantial nuclear deformation, increase lamin-A levels and promote osteogenic differentiation. The findings of this study demonstrate a so far missing link between 3D surface curvature and hMSC behavior. This will not only help to better understand the role of extracellular matrix architecture in health and disease but also give new insights in how 3D geometries can be used as a cell-instructive material parameter in the field of biomaterial-guided tissue regeneration.

Differentiation of adipose stem cells seeded towards annulus fibrosus cells on a designed poly(trimethylene carbonate) scaffold prepared by stereolithography.

Cell-based therapies could potentially restore the biomechanical function and enhance the self-repair capacity of annulus fibrosus (AF) tissue. However, choosing a suitable cell source and scaffold design are still key challenges. In this study, we assessed the in vitro ability of human adipose stem cells (hASCs), an easily available cell source to produce AF-like matrix in novel AF-mimetic designed scaffolds based on poly(trimethylene carbonate) and built by stereolithography. To facilitate efficient differentiation of hASCs towards AF tissue, we tested different culture medium compositions and cell seeding techniques. This is the first study to report that medium supplementation with transforming growth factor (TGF)-ß3 is essential to support AF differentiation of hASCs while TGF-ß1 has negligible effect after 21 days of culture. Fibrin gel seeding resulted in superior cell distribution, proliferation and AF-like matrix production of hASCs compared to direct and micromass seeding under TGF-ß3 stimulation. Not only the production of sulphated glycosaminoglycans (sGAG) and collagen was significantly upregulated, but the formed collagen was also oriented and aligned into bundles within the designed pore channels. The differentiated hASCs seeded with fibrin gel were also found to have a comparable sGAG:collagen ratio and gene expression profile as native AF cells demonstrating the high potential of this strategy in AF repair. Copyright © 2016 John Wiley & Sons, Ltd.

µCT based assessment of mechanical deformation of designed PTMC scaffolds.

BACKGROUND: Advances in rapid-prototyping and 3D printing technologies have enhanced the possibilities in preparing designed architectures for tissue engineering applications. A major advantage in custom designing is the ability to create structures with desired mechanical properties. While the behaviour of a designed scaffold can be simulated using bulk material properties, it is important to verify the behaviour of a printed scaffold at the microstructure level. OBJECTIVE: In this study we present an effective method in validating the mechanical behaviour of designed scaffolds using a µCT with an in-situ mechanical deformation device. METHODS: The scaffolds were prepared from biodegradable poly(trimethylene carbonate) (PTMC) by stereolithography and images obtained using a high-resolution µCT with 12.25µm isometric voxels. The data was processed (filtering, segmentation) and analysed (surface generation, registration) to extract relevant deformation features. RESULTS: The computed local deformation fields, calculated at sub-pore resolutions, displayed expected linear behaviour within the scaffold along the compressions axis. On planes perpendicular to this axis, the deformations varied by 150- 200µm. CONCLUSIONS: µCT based imaging with in-situ deformation provides a vital tool in validating the design parameters of printed scaffolds. Deformation fields obtained from micro-tomographic image volumes can serve to corroborate the simulated ideal design with the realized product.

Surface properties and interaction forces of biopolymer-doped conductive polypyrrole surfaces by atomic force microscopy.

Surface properties and electrical charges are critical factors elucidating cell interactions on biomaterial surfaces. The surface potential distribution and the nanoscopic and microscopic surface elasticity of organic polypyrrole-hyaluronic acid (PPy-HA) were studied by atomic force microscopy (AFM) in a fluid environment in order to explain the observed enhancement in the attachment of human adipose stem cells on positively charged PPy-HA films. The electrostatic force between the AFM tip and a charged PPy-HA surface, the tip-sample adhesion force, and elastic moduli were estimated from the AFM force curves, and the data were fitted to electrostatic double-layer and elastic contact models. The surface potential of the charged and dried PPy-HA films was assessed with Kelvin probe force microscopy (KPFM), and the KPFM data were correlated to the fluid AFM data. The surface charge distribution and elasticity were both found to correlate well with the nodular morphology of PPy-HA and to be sensitive to the electrochemical charging conditions. Furthermore, a significant change in the adhesion was detected when the surface was electrochemically charged positive. The results highlight the potential of positively charged PPy-HA as a coating material to enhance the stem cell response in tissue-engineering scaffolds.